Background/Objectives: Previous studies have identified several determinants of multimorbidity, but social factors remain unclear. Therefore, we aimed to explore the association between social and lifestyle factors and the risk of developing multimorbidity in middle-aged population from the United Kingdom.

Methods: This prospective study uses data from the UK Biobank cohort, comprising 407,115 participants recruited from 2006 to 2010 and followed up until May 31, 2022. Multimorbidity was defined as having two or more chronic diseases. Cox proportional hazards models were conducted to analyse the association between social and lifestyle factors and the risk of developing multimorbidity, adjusting for sociodemographic and anthropometric characteristics.

Results: A total of 33,794 participants developed multimorbidity during a median follow-up of 13.2 years. The baseline mean age was 56.2 years [standard deviation (SD) = 8.08], and 54.6% of participants were women. In the fully adjusted models, loneliness [hazard ratio (95% confidence interval) = 1.30 (1.25-1.36), social isolation [HR (95%CI) = 1.15 (1.11-1.19)], previous [HR (95%CI) = 1.25 (1.22-1.28)] and current smokers [HR (95%CI) = 2.10 (2.04-2.17)], non-optimal sleep duration [HR (95%CI) = 1.23 (1.20-1.26)], high sedentary lifestyle [HR (95%CI) = 1.22 (1.19-1.25)], and high meat intake [HR (95%CI) = 1.09 (1.06-1.11)] were associated with an increased risk of incident multimorbidity.

Conclusions/Recommendations: Loneliness, social isolation and lifestyle factors contribute to the risk of developing multimorbidity. This study emphasizes the importance of adopting a comprehensive approach that considers social and lifestyle factors as a primary predictor of multimorbidity.

Funding: PI 20/1040, PI 23/272 from the Instituto de Salud Carlos III (Spanish Ministry of Science and Innovation, Madrid, Spain), and European Regional Development Fund-ERDF. D. González-Beltrán has received a predoctoral contract from Universidad Autónoma de Madrid (FPI-UAM). A. Vázquez-Fernández holds a “Training of University Professors - FPU” grant (FPU20/5466) from the Spanish Ministry for Universities.